Many manufacturing operations utilize plasma processing. Plasma-enhanced Vapor Deposition (PVD), for example, is increasingly used for deposition of thin metallic and non-metallic films. Most PVD systems are either of the cathodic arc or sputtering types. While the arc discharge plasma utilized in a cathodic arc PVD systems is characterized by high currents and low voltages, the glow plasma utilized in sputter PVD systems is characterized by lower currents and higher voltages. Sputter PVD systems often include features that provide magnetic fields to support electric field ionization of the glow plasma.
A glow plasma and an arc discharge plasma, under appropriate conditions, can exhibit mode shifts. For example, a glow plasma can transition to an arc discharge plasma, while, though unlikely, an arc discharge plasma can transition to a glow plasma.
Undesired arcing is a significant problem for the performance of sputter PVD systems. Arcing can be caused by a variety of factors. For example, arcing might be caused by flaking of the target during sputtering, overheating of the target, a gas disturbance within the plasma, or impurities in either the inert gas utilized to form the plasma or the target material. Inherently, plasma noise produces a certain amount of “micro-arcing” within a glow plasma inside the deposition chamber. However, the micro-arcing may develop into more severe plasma arcing, or “hard arcing”, within the chamber. An arc can remove the poisoning from the target, but it may also generate undesirable particles.
Some systems cope with arcing by shutting down the power supply when an arc is detected. For example, detection of a severe arc can cause the power supply to momentarily interrupt its output, for example, for 0.100–25 msec. Arcing current fluctuations, however, can have a frequency in the order of 1–10 MHz (i.e., a duration of 0.1–1.0 μsec).
Some power supplies may exacerbate the problems associated with plasma arcing. For example, a DC power supply can have energy stored in an output stage, such as in an output filter. Upon the appearance of micro-arcing or arcing conditions, the stored energy may be discharged into the sputtering chamber. The discharged energy pulse has a duration of approximately 0.2–20 μsec, which is too rapid to be controlled or limited by common detection circuitry of the power supply.
Some systems periodically interrupt or apply a voltage reversal of the cathode voltage in an attempt to avoid arcing. The deposition rate may be reduced, however, because the cathode voltage is not continuously applied. Moreover, periodic suppression circuitry adds significant cost. Periodic suppression systems are usually employed when defect free deposition is required, such as in the manufacture of semiconductors.